1. Field of the Invention
The present invention relates to a power tool that performs a predetermined operation by driving a tool bit.
2. Description of the Related Art
Japanese laid-open patent publication No. 2008-173739 discloses a screw tightening machine having a power transmitting mechanism in the form of a planetary gear mechanism that transmits torque of a motor to a tool bit at reduced speed. Such a screw tightening machine having a planetary gear mechanism is advantageous, for example, in that a large speed reduction ratio and a strong screw-tightening force can be obtained and in that an input shaft and an output shaft can be coaxially disposed.
In the gear type speed reducing mechanism, however, backlash is inevitable and causes noise, which is particularly remarkable in a speed reducer which rotates at high speed.